After you've done Mr. Bakers suggestion, a few other possibles could be...
-Take both positive and negative terminals off the battery for 15 minutes. Put them back on and see if it clears.
-Sometimes even corrosion around the terminals can throw the sensor off. Can be cleaned up with baking soda and water.
-check ground wires.
-Can also take the battery out of the harness to check to see if any debre or wiring is crimped around the housing.